Technical Field
The present invention relates to an ignition coil for an internal-combustion engine for generating an ignition spark at a spark plug.
Related Art
An ignition coil is known that includes an assembly of a primary coil, a secondary coil, and a central core, and a ring-shaped outer core having the assembly inserted therein. In such an ignition coil, an axial end surface of the central core is in contact with an inside surface of the outer core, and a core gap is formed between an opposite axial end surface of the central core and the inside surface of the outer core.
For example, Japanese Patent Application Laid-Open Publication No. 1991-224207 discloses an ignition coil for an internal-combustion engine including a first core having a primary coil and a secondary coil disposed on an outer circumference of a first core and a second core surrounding the first core to form a closed flux path together with the first core. The above disclosed ignition coil has a core gap formed between an axial end surface (referred to as a second axial end surface) of the first core and the second core with an opposite axial end surface (referred to as a first axial end surface) of the first core pressed against a contact surface of the second core. This can prevent a gap between the first axial end surface of the first core and the contact surface of the second core from occurring, thereby preventing degradation in performance of the ignition coil or reducing variations in performance of the ignition coil.
In the ignition coil disclosed in Japanese Patent Application Laid-Open Publication No. 1991-224207, when the assembly of the primary coil, the secondary coil, and the first core is inserted into the second core from an opening of the second core, the assembly may be inserted oblique to the opening of the second core with the first axial end surface of the first core kept in contact with the inside surface of the second core. During insertion of the assembly into the second core, an end surface of a primary spool having the primary coil wound therearound may contact the inside surface of the second core to be abraded until the first axial end surface of the first core becomes in contact with the contact surface of the second core, which may cause variations in abraded quantity of the primary spool. Although the first core is in contact with the second core, tilting of the first core when assembled in the second core may cause variations in amount of magnetic flux passing through the first and second cores, which may degrade the performance of the ignition coil or cause variations in performance of the ignition coil.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing an ignition coil for an internal-combustion engine, capable of vertically inserting an assembly of a primary coil, a secondary coil, and a central core into an outer core so that substantially no tilting of the central core when assembled in the outer core occurs.